The method according to the present invention is a development of the method disclosed in Danish patent application No. 1592/88, filed 23 Mar. 1988, and the corresponding PCT-application No. PCT/DK89/00065 (WO 89/09288), and relating to a method for preparing a mixture of fructose, glucose and compounds of the general formula GF.sub.n, wherein G is glucose and F is fructose and n is an integer, said mixture comprising calculated as dry matter 10-20% by weight of G+F+GF, 10-20% by weight of GF.sub.2, 8-15% by weight of GF.sub.3, and 72-45% by weight of GF.sub.4 and above by recovering said mixture from plant tubers or roots by means of a method which does not involve any chemical modification of the components of the mixture.
The mixture prepared according to DK patent application No. 1592/88 is useful as a low-calorie material with sweet taste.
Sucrose has heretofore been widely used in confectionary and food by virtue of its excellent characteristics, such as good sweetness, body, taste and crystallinity. Sucrose, however, constitutes a substrate for dextransucrase produced by intraoral microorganisms, and, as a result, consecutive intake of sucrose leads to formation of large amounts of insoluble dextran in the mouth. Thereby formation of dental plaque is accelerated. Therefore, sucrose is said to possess cariogenicity. Recently, there has been a trend to reduce the calorie intake for prevention of obesity and a low-calorie sweet material, instead of a high-calorie one, such as sucrose, has been demanded.
For this reason many suggestions have been made as to find a sweet material for replacing sucrose, such as the artifical sweeteners saccharin, cyclamate, aspartame, sorbitol and many others.
Such alternative sweeteners are widely used but also possess several disadvantages, such as a bitter tang or aftertaste. Furthermore, some of the artificial sweeteners are suspected to be carcinogenic.
These disadvantages, especially the suspicion of being carcinogenic--a recurrent subject in the public debate--have made consumers reluctant to use products containing any type of artificial sweetener.
It is known that the dahlia tubers contain a polysaccharide known as inulin. According to Merck Index, 10th edition, Merck & Co. Inc., Rahway, N.J., U S A, 1983, p. 725, Index No. 4872, it has the formula GF.sub.n with n being of an average value of approx. 37. The preparation of inulin from dahlia tubers is disclosed in U.S. Pat. No. 4,285,735.
It is also known that chicory roots and Jerusalem artichoke tubers contain corresponding polysaccharides or oligosaccharides with the general formula GF.sub.n. The value of n varies depending on the raw plant material in question, cf. e.g. S. E. Fleming et al. Preparation of high-fructose syrup from the tuber of the Jerusalem artichoke (Helianthus tuberosus L.), CRC Crit. Rev. Food Sci. Nutr., 11, 1-23, 1979, U.S. Pat. No. 4,613,377 and EP patent application No. 0 201 676/A2.
The interest in these polysaccharides and oligosaccharides in form of inulin or inulin-like compounds (inulides) has until now been directed to the large contents of fructose moities in said compounds. They are thus a useful source for the preparation of fructose, especially with regard to using fructose as nutrient replenisher and sweetener.
EP patent application 0 201 676 discloses a method for preparing a low-glucose cleavage product from plant parts, said cleavage product comprising inulin-like oligo- or polysaccharides. According to this method the extracted oligo- or polysaccharides are subjected to treatment with the enzyme inulinase in order to decompose them to fructose and fructose-oligomers.
U.S. Pat. No. 4,613,377 discloses a method where the inulin-like oligosaccharides obtained from Jerusalem artichoke tubers or chicory roots are subjected to partial or substantially complete hydrolysis.
Further prior art disclosing the general state of the art comprises the following.
GB patent No. 1,405,987 discloses the preparation of a mixture of fructose and glucose, i.e. invert sugar, by crystallization.
U.S. Pat. No. 2,555,386 discloses the preparation of inulin from Jerusalem artichoke. The inulin obtained is used as a substitute for starch and for the preparation of levulose and alcohol.
U.S. Pat. No. 4,138,272 discloses a method for the preparation of fructose from xerophyte plants, for example agave.
DE Offenlegungsschrift No. 3,211,776 discloses a method for obtaining juice from Jerusalem artichoke to be used for the preparation of hydrocarbons, for example acetone butanol.
Derwent's abstract No. 87-305.414/43, SU patent application No. 306,061 (SU patent No. 1,300,032) discloses the preparation of fructose from Jerusalem artichoke.
Non-patent literature concerning the analyses of "inulin" from Jerusalem artichoke is mentioned in
Chemical Abstracts (CA), vol. 26, (1932), p. 5355, Food Ind. 4, 66-9(1932); PA1 CA, vol. 29, (1935), p. 8387, Sovet. Sakhar 1935, No. 1, 4-47; PA1 CA, vol. 50, ( 1956), col. 13152 g, Trudy Komissii Anal. Khim., Akad. Nauk. S.S.S.R., Inst. Geokhim. i Anal. Khim. 6, 492-7(1955); PA1 CA, vol. 51, (1957), col. 9813 a, Zucker-Beih. 3, 86-94(1957); PA1 CA, col 53, (1959), col. 18189 c, Cukoripar 12, 126-9(1959). PA1 1. filtration followed by adjusting the pH value by adding CO.sub.2 or phosphoric acid and subsequent filtration, or PA1 2. adding CO.sub.2 or phosphoric acid and subsequent filtration, i.e. the extract is only filtered once. PA1 a) the substantially cleaned tubers or roots are cut into cosettes, PA1 b) the cosettes are subjected to extraction with water, PA1 c) the extract, or juice, is treated in a suitable order one or more times by each of the following steps: PA1 d) the juice from step c) is subjected to ion exchange, PA1 e) the juice from step d) is optionally treated with active carbon, PA1 f) the juice from step d) or e) is optionally concentrated by hyperfiltration, PA1 g) the juice from step d), e) or f) is evaporated to a syrup with a dry matter content of 91-96% by weight, PA1 h) the syrup is dried to a powder. PA1 i) the syrup is distributed as a thin layer on a cooling surface with a temperature of below 0.degree. C., preferably between minus 10.degree. C. and 0.degree. C., whereby the syrup solidifies to a hard, glass-like mass, PA1 k) the hard, glass-like mass formed in step i) is scraped off the cooling surface in form of flakes, PA1 1) the flakes are roughly ground and PA1 m) the roughly ground flakes are dried at a temperature of below 60.degree. C. to a dry matter content of above 96% by weight, preferably above 97% by weight, or PA1 n) the temperature of the syrup is adjusted to a value below the boiling point of said syrup at atmospheric pressure, PA1 o) the syrup is fed into a vacuum chamber, PA1 p) the syrup is led through the vacuum chamber without any heat supply to the syrup, PA1 q) the obtained dried or evaporated mixture is removed from the vacuum chamber through an air lock. PA1 0-10% by weight of G+F+GF, PA1 5-20% by weight of GF.sub.2, PA1 5-15% by weight of GF.sub.3, PA1 5-15% by weight of GF.sub.4, PA1 5-15% by weight of GF.sub.5, and PA1 80-25% by weight of GF.sub.6 and above. PA1 a) cutting the substantially cleaned tubers or roots into cosettes, PA1 b) subjecting the cosettes to extraction with water, PA1 c) treating the extract, or juice, in a suitable order one or more times by each of the following steps: PA1 d) subjecting the juice from step c) to ion exchange, PA1 e) optionally treating the juice from step d) with active carbon, PA1 f) optionally concentrating the juice from step d) or e) by hyperfiltration, PA1 g) optionally evaporating the juice from step d), e) or f) to a syrup, and PA1 h) optionally drying the syrup to a powder,
GB patent applications Nos. 2,072,679, 2,105,338 and 2,179,946 disclose a low-calorie sweet material comprising a mixture of oligosaccharides with 1-4 molecules fructose bound to sucrose, i.e. a mixture of the oligosaccharides GF.sub.2, GF.sub.3, GF.sub.4 and GF.sub.5. The above mixture is prepared by stepwise synthesis from sucrose letting the enzyme fructosyl transferase act upon sucrosa: ##STR1##
This synthesis is expensive and yields only small amounts of the oligosaccharides GF.sub.4 and GF.sub.5. Moreover, the above reaction 1) results in the production of an excess of glucose. The known sweet material is available under the name "Neosugar", both in form of a syrup and a powder. "Neosugar" does not possess the detrimental effects of sucrose or alternative artificial sweeteners mentioned above. Its preparation is, however, too expensive to allow wide use thereof. Furthermore, consumers are probably reluctant to use the product if presented as a chemically modified product.
Prior to DK patent application No. 1592/88 there was thus a need for a method allowing the preparation of a sweetener on the basis of a natural mixture without the detrimental effects of sucrose and conventional alternative sweeteners, said method being inexpensive and not involving chemical modification of the desired natural components in the starting materials.
It was shown that a material in form of a mixture of saccharides satisfying these needs could be prepared from a natural raw material, i.e. plant tubers or roots, e.g. tubers of the Jerusalem artichoke, Helianthus tuberosus L. or roots of chicory, Cichorium.
Accordingly DK patent application No. 1592/88 discloses a method for preparing a mixture of fructose, glucose and compounds of the general formula GF.sub.n, wherein G is glucose and F is fructose and n is an integer, said mixture comprising calculated as dry matter 10-20% by weight of G+F+GF, 10-20% by weight of GF.sub.2, 8-15% by weight of GF.sub.3, and 72-45% by weight of GF.sub.4 and above by recovering said mixture from plant tubers or roots by means of a method which does not involve any chemical modification of the components of the mixture.
By using the above method it is possible to prepare the mixture of saccharides in form of a dry powder at a price of less than half the costs involved in the preparation of the mixture known from GB patent application No. 2,072,679 according to the methods disclosed in GB patent applications Nos. 2,072,679, 2,105,338 and 2,179,946.
The composition of the mixture prepared by the above method differs from the composition of inulin derived from dahlia tubers by having a lower degree of polymerisation. Thus the ratio F/G is 3-4 for the above as compared to inulin where the ratio F/G is approx. 30.
An essential requirement for any material used as sweet material is its water-solubility. The above mixture has a composition or degree of polymerisation within such limits that, on the one hand, the constituents are sufficiently large to pass predominantly undigested through the alimentary tract. On the other hand, the constituents are still water-soluble. The inulide mixture obtained from dahlia tubers is not soluble in water in its unmodified form, and has thus to be subjected to chemical or other modification, such as hydrolysis, if a water-soluble product is desired.
The mixture prepared according to the above method has a good combination of sweetening effect, water solubility and indigestibility. However, when the sweetening effect is of minor importance and/or an especially low calorie content is desired it would be desirable to reduce the content of fructose, glucose and sucrose.
The method according to DK patent application No. 1592/88 is described in greater detail below.
The mixture is obtained from plant tubers or roots, preferably tubers, of Jerusalem artichoke (Helianthus tuberosus L.) or roots of chicory because these plants give a high yield of the mixture of the mentioned composition. When the Jerusalem artichoke is cultivated in a temperate climate the tubers harvested during the major part of the harvesting season result in a mixture of a almost constant composition.
The mixture is advantageously prepared in form of a dry powder, thus enabling an easier handling and a more stable product. It is, however, also possible to use the mixture in form of a juice or syrup, especially for industrial use, when shipment in large amounts, e.g. in a tank, directly to the user is possible and convenient. In this case the problems in connection with the removal of the remaining water are avoided.
The mixture can be prepared from Jerusalem artichoke tubers or roots of chicory by first preparing a syrup, i.e. a concentrated solution with a dry matter content of between 65 and 80% by weight. The syrup is then evaporated further and dried until the desired powdery product is obtained.
Syrup from Jerusalem artichoke tubers or roots of chicory can be prepared in a manner resembling conventionally used methods for the preparation of sucrose syrup from sugar beets. It is thus possible to perform this part of the production with a conventional sugar beet plant. This is advantageous in that the capacity of existing plants is considerably larger than is demanded on the world market. It is thus possible to use this free capacity for the preparation of the inulide mixture.
Syrup from Jerusalem artichoke tubers or roots of chicory is prepared as follows. Stones, green parts and soil are removed from Jerusalem artichoke tubers or roots of chicory and the tubers or roots are cut into cosettes. These are extracted with water in a so-called DDS-diffusor, i.e. a trough with a steam mantle. The trough has a small inclination and is provided with a twin screw for the transport of the cosettes counter to the flow of water. The extraction is performed at 60.degree.-85.degree. C. and the desired mixture is transferred to water in dissolved form. Part of the protein content is denaturated, thus rendering it insoluble. Enzymes present in the solution are also denaturated and thus inactivated so that they cannot decompose the desired mixture. The aqueous extract has a dry matter content of 10-17% by weight.
Impurities, such as pectin, proteins and cell material, are removed from the extract by adding slaked lime, Ca(OH).sub.2, up to a pH-value of 10.5-11.5. After adding the slaked lime the following alternatives are open:
In a further embodiment the extract is treated with slaked lime in two steps, i.e. it is subjected to a pretreatment and to a main treatment with slaked lime. Then CO.sub.2 is added followed by filtration. Then CO.sub.2 is added again followed by filtration. The above filtration steps can of course also be carried out by technically equivalent separation methods.
Salts and colours may be removed by means of ion exchange. Residues of colours and undesired taste and odoriferous compounds may be removed by subsequent treatment with active carbon.
The purified extract with a dry matter content of 8-14% by weight can be subjected to hyperfiltration (reverse osmosis) in order to remove water up to a dry matter content of approx. 25-30% by weight. In a multi-step evaporator, such as a falling film evaporator, the extract is subsequently concentrated to a syrup with a dry matter content of 75-85% by weight.
This syrup is further evaporated to a dry matter content of 91-96% by weight by means of evaporation e.g. in a vertical vacuum dryer or a thin film evaporator.
On the basis of such a syrup the mixture is prepared in form of a dry powder by using one of two alternative methods, i.e. one termed "drying with quenching" and one termed "vacuum flash drying". These methods are generally suitable for the concentration of syrup-like materials, and are subject matter of the DK patent applications Nos. 1593/88 and 1594/88, respectively, both filed 23 Mar. 1988.
It is thus possible to prepare the above inulide mixture in form of a dry powder. Such a dry powder is bacteriologically stable. High osmotic pressure is required for obtaining bacteriological stability. For the relatively high molecular weight oligosaccharides a high osmotic pressure is first obtained at a high dry matter content.
A liquid mixture with a sufficiently high dry matter content is difficult to handle in the preparation step as well as during the application of said mixture, as it has an almost paste-like consistency resembling soft toffee mass. Consequently such a mixture flows very slowly without solidifying and is very sticky. As mentioned above, however, it is possible to use the mixture in form of a juice or syrup if the above problems are of no importance, e.g. in case of industrial use in large amounts.
The dry mixture obtained by one of the methods disclosed in DK patent applications Nos. 1593/88 and 1594/88 can successfully be used as a partial or complete substitute for sugar and other sweet materials including sorbitol.
The method for the preparation of the mixture in form of a dry powder comprises carrying out the following steps:
1) addition of Ca(OH).sub.2, PA2 2) addition of CO.sub.2 or phosphoric acid, and PA2 3) filtration, PA2 1) addition of Ca(OH).sub.2, PA2 2) addition Of CO.sub.2 or phosphoric acid, and PA2 3) filtration
For overcoming the difficulties during the evaporation of the high-concentrate syrup, step h) is advantageously carried out by one of the following methods, i.e. either
If it is possible to use the mixture as a juice, only the above steps a)-f) is carried out. Then the juice can be evaporated to a syrup if desired. In this way the problems connected with removing remaining water are avoided.
As mentioned before, there is a demand for removing or at least reducing the content of mono- and disaccharides, in the mixture of inulides prepared according to DK patent application No. 1592/88. This is due to i.a. the above-mentioned desire to reduce the calorie content and cariogenic effect of lower saccharides, while at the same time retaining the preferred inulides. Accordingly, the inulide compounds of formula GF.sub.2 and above are especially desirable. Such compounds are beneficial to ones health, since, like fibers, they pass the alimentary tract without being digested. In contrast to the result of ingestion of lower saccharides a violent increase of the glucose level is avoided, the latter being an important risk factor with diabetes. At the same time the preferred inulides support the growth of bacteria of the genus Bifidobacterium naturally occuring in the intestinal flora. Moreover the preferred inulides act as bulking agents in foodstuffs. This is of particular importance for an attractive texture of the foodstuff in question. On the other hand, it can also be desirable to remove higher oligosaccharides, such as GF.sub.n, n&gt;10, to improve the water-solubility of the mixture.